Transgenic mice expressing mutant Notch3 develop vascular alterations characteristic of cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is an increasingly recognized adult-onset autosomal dominant vascular dementia, caused by highly stereotyped mutations in the Notch3 receptor. CADASIL is a widespread angiopathy characterized by a degeneration of vascular smooth muscle cells (VSMCs) and the abnormal accumulation of electron-dense granular material called GOM and Notch3 protein, because of an impaired clearance. Evidence that VSMCs are the primary target of the pathogenic process is supported by the restricted expression of Notch3 in these cells but mechanisms of their degeneration remain essentially unknown. We generated transgenic mice in which the SM22alpha promoter drove, in VSMCs, the expression of a full-length human Notch3 carrying the Arg90Cys mutation, a CADASIL archetypal mutation. Transgenic mice showed no evidence of prominent brain parenchyma damage but demonstrated the two hallmarks of the CADASIL angiopathy, GOM deposits and Notch3 accumulation, within both the cerebral and peripheral arteries. Of interest, arteries of the tail were more severely affected with prominent signs of VSMC degeneration. Time-course analysis of vessel changes revealed that disruption of normal VSMC anchorage to adjacent extracellular matrix and cells, VSMC cytoskeleton changes as well as starting signs of VSMC degeneration, which were detected around 10 months of age, preceded Notch3 and GOM accumulation appearance, which were observed only by 14 to 16 months of age. In conclusion, we have generated transgenic mice that recapitulate the characteristic vascular lesions observed in CADASM. Our results indicate that Notch3 or GOM accumulation are unlikely to be the prerequisites for the induction of VSMC degeneration and suggest that degeneration of VSMCs may rather be triggered by the disruption of their normal anchorage, based on the important role of adhesion for cell survival.